Tillage and evaporativity effects on the drying characteristics of a silty loam: Evaporation prediction models

Evaporation of water from 'micro-lysimeters' collected from four types of field tillage treatments, namely, ploughed to a depth of 30cm (P), ploughed and then harrowed (P + H), ploughed, harrowed and rolled (P + H + R) and untilled (UNT) plots, was studied in a controlled laboratory environment at five rates of atmospheric evaporativity close to those found under field conditions. Evaporative demand (E(o)) in the field was determined by measuring evaporation from open water with a recording evaporation balance. Actual evaporation from the field soil was determined by daily measurement of water content in the top 10 and 20cm layers. Drying was best described by a modified version of the square root of time behaviour model of T.A. Black, W.R. Gardener and G.W. Thurtell (The prediction of evaporation drainage and soil water storage for a bare soil. Soil Sci. Am. Proc., 33: 655-660, 1969) and a simple parametric model similar to that proposed by J.J.T.I. Boesten and L. Stroosnijder (Simple model for daily evaporation from fallow tilled soil under spring conditions in a temperate climate. Neth. J. Agric. Sci., 34: 75-80, 1986). The parametric model was incorporated in a model describing water dynamics in a silt loam soil (Typic Hapludalf) on field plots located near Ter Munck, 5 km southwest of Leuven, Belgium. The results show that drying characteristics of tilled soils are influenced by factors such as tillage depth, surface micro-relief, soil type, and the nature of the evaporative demand, and that it is possible to incorporate such effects in evaporation models. However, more research is needed to study the combined effects of tillage type and depth and atmospheric evaporativity on the drying characteristics of different soils, and to compare the relative effect of radiation-dominated evaporativity on the evaporation parameters with that of wind-dominated evaporativity

A simple Micro-relief Meter for Estimating Surface Roughness and Rilled Layer Porosity

A simple micro-relief meter which can be operated by one person and be used both in the field and the laboratory was designed and used to measure the surface micro-relief of ploughed (P), ploughed and then harrowed (PH), and ploughed, harrowed and then rolled (PHR) soils. The measurements were used to estimate the plough layer porosity of the tilled soils. The estimated values of tilled layer porosity (P) were compared with those determined in a laboratory from 100 cubic cm core samples and from water retention curves (WRC) of the soils. The results showed that both WRC and core methods gave significantly lower values of P for the ploughed soil, which the WRC method consistently gave lower values of P for all the tilled soils. The results indicated that such a meter can be used to characterize surface roughness of tilled soils and that the micro-relief measurement method can give reasonable estimates of the porosity of freshly tilled soils with rough structures dominated by large clods and often loose soil material. UNISWA Research Journal of Agriculture, Science and Technology Vol 3 (1) 1999: pp 21-2

Vegetation Dynamics of Sloping Lands under Different Grazing Pressures in the Highlands of Ethiopia

The impact of livestock grazing on the dynamics of vegetation species in the highland slopes of Ethiopian was studied. This was done by analyzing vegetation species germinating from cattle dung collected from the slopes at different times and comparing these species with those found on the pastures the animals regularly grazed. It was observed that grazing had little effect on the species richness of pastures above 3% slope while moderate and heavy grazing increased bio-diversity of pastures found on 2-3% slopes. However, heavy grazing pressure resulted in good grazing ever, heavy grazing pressure resulted in good grazing quality species being replaced by poor quality species. The effect of grazing on vegetation dynamics of the pastures was complicated by the fact that cow dung was often collected for fuel, and that at certain times, animals moved to higher slopes outside the study area. Further research is needed to determine where the animals go and what type of vegetation species they graze whenever they leave to confines of the pastures studied here, and to ascertain the dormancy and viability of the seeds of the various vegetation species when they pass through the rumens of the animals in order to get a clearer picture on the effects of grazing on vegetation dynamics. UNISWA Research Journal of Agriculture, Science and Technology Vol. 4 (1) 2000: pp 44-5

Hydrologic response to cattle grazing in the Ethiopian highlands

The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the 1995 rainy season in the Ethiopian highlands. The study was conducted on 0.01 ha plots established on sites with 0-4 percent and 4-8 percent slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animals-unit-months (AUM) ha-1; moderate grazing stocked at 1.8 AUM ha-1; heavy grazing stocked at 3.0 AUM ha-1; very heavy grazing stocked at 4.2 AUM ha-1; very heavy grazing on ploughed soil stocked at 4.2 AUM ha-1; and a control with no grazing. Heavy to very heavy grazing pressure significantly increased surface runoff and soil loss and reduced infiltrability of the soil. It was observed that fine textured soils were more susceptible to trampling effects than coarse textured soils, and that reduction in infiltration rates was greater on soils which had been tilled and exposed to very heavy trampling. The problems of high runoff and erosion rates on the upper slopes is likely to be exacerbated by the fact that during the rainy season higher grazing pressure is exerted on the upper than lower slopes. Sediments produced from the highlands, which form headwaters of major rivers in the region, are modifications, the plot design presented here can be used for assessing livestock impacts on natural resources on different landforms at large scales such as watersheds. How the same amount of livestock mass dispersed by different livestock species impacts on the grazing lands needs to be studied further

Land degradation and intensified livestock and crop production in the Ethiopian highlands

The Ethiopian highlands are ecologically heterogenous and densely populated by humans and animals. Due to the high human population pressure and large herds of livestock on small farm areas, continuous overgrazing of natural grasslands is common. In attempts to meet the increasing food and feed demands of large human and livestock populations, respectively, farmers are cultivating more land permanently, grazing lands have been encroached and many traditional farming systems have broken down. Apart from keeping a mix of animals, particularly oxen to supply farm power requirements, farmers in the highlands cultivate a complex mix of crops for subsistence. ILRI's collaborative research with national partners, NGOs and other IARCs in the Ethiopian highlands has focussed on generating environmentally safe technologies for improving the welfare of resource-poor smallholder farmers who depend on crop-livestock production systems across the fragile highland ecologies of East Africa

Infiltration rates, surface runoff, and soil loss as influenced by grazing pressure in the Ethiopian highlands

The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the rainy season of 1995 in the Ethiopian highlands. The study was conducted at two sites with 0-4 percent and 4-8 percent slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-months (AUM)/ha; moderate grazing stocked at 1.8 AUM/ha; heavy grazing stocked at 3.0 AUM/ha; very heavy grazing stocked at 4.2 AUM/ha; very heavy grazing on ploughed soil stocked at 4.2 AUM/ha; and a control with no grazing. Heavy to very heavy grazing pressure significantly reduced biomass amounts, ground vegetative cover, increased surface runoff and soil loss, and reduced infiltrability of the soil. Reduction in infiltration rates was greater on soils which had been ploughed and exposed to very heavy trampling. It was observed that, for the same percent vegetative cover, more soil loss occurred from plots on steep than gentle slopes, and that gentle slopes could withstand more grazing pressure without seriously affecting the ground biomass regeneration compared to steeper slopes. Thus, there is a need for developing `slope-specific' grazing management schedules particularly in the highland ecozones rather than making blanket recommendations for all slopes. More research is needed to quantify annual biophysical changes in order to assess cumulative long-term effects of grazing and trampling on vegetation, soil, and hydrology of grazing lands. Modelling such effects is essential for land use planning in this fragile highland environment

Biophysical and hydrological changes in soils under livestock grazing varying slopes in the East African highlands

The impacts of grazing on biophysical and hydrological properties of grazing lands were investigated on two sites represting 0-4 percent and 4-8 percent slopes at the Livestock research Institute (ILRI) Debre Zeit research station, 50 km South of Addis Ababa. Grazing pressure differently influence ground vegetative cover, increased surface runoff and soil loss, and reduced water infiltrability of the soil between the two land slopes. Grazing management strategies need to be `slope-specific' and more research is needed to quantify biophysical changes in order to asses cumulative long term effects of grazing and trampling on vegetation, soil, and hydrology of grazing lands and complement efforts that seek to cohesively and compatibly manage land resources to sustainably serve multiple needs of communities

Biomass requirements from natural pastures for livestock grazing and soil protection in the Eastern African highlands

The problem of seasonal shortages of herbage production from natural pastures in the Ethiopian highlands was investigated. This was done by comparing the available biomass amounts on the pastures with biomass amounts required for livestock grazing and for protecting land slope from soil erosion within a given slope limit at different times of the year. It was observed that the pattern of biomass availability and the requirements for livestock grazing and soil protection vary seasonally, as grazing is concentrated in different parts of the watershed at different times. It was further observed that from March to September feed supplementation is necessary since the available biomass quantities from natural pastures and crop residues on slopes above 3 % are generally inadequate to meet livestock and soil protection requirements. However, with changes in the grazing management to regulate grazing pressure, herbage production on these slopes may be increased to adequately meet livestock needs while protecting the soil from erosion. Herbage production could further be improved through fertilizer application, provision of feed supplements during times of shortfall in biomass, and/or by leaving animal dung on the pasturelands instead of collecting it for fuel and other uses. The cost of feed supplements relative to the cost of restoring degraded land as a result of allowing grazing to exceed the safe limits should be investigated. UNISWA Jnl of Agric Vol 8 1999: pp 23-3

The effect of livestock grazing on surface runoff and soil erosion from sloping pasture lands in the Ethiopian highlands

Efffects of livestock grazing on surface runoff and soil erosion at varying slopes were studied in pasture lands within Ginchi watershed, Ethiopia. The results showed that livestock grazing in the watershed followed distinct seasonal and spatial patterns during the rainy season, grazing pressure was greatest on the upper slopes (>5 percent slope) while the pressure shifted to the lower slopes during part of the dry season. Seasonal grazing pressure in different parts of the watershed was further complicated by the fact that during the rainy season and immediately after the rains, grazing was limited to individually designated pasture lands while during most part of the dry season, the entire watershed became a common grazing resource for livestock of watershed residents as well as those farmers outside the watershed. It was observed that, on pasutres above 4.2 percent slope, there is the risk of erosion rates exceeding the estimated soil loss tolerable limit under the current grazing pressures (heavy grazing), while slopes exceeding 5.8 percent are likely to suffer soil erosion under moderate grazing pressure at the current level of biomass productivity. Since livestock are mobile, farmers tend to take advantage of this attribute by seasonally moving the livestock to different parts of the watershed. This study has demonstrated the need for better understanding of the resource use patterns beyond the individual farmlands, most preferably at watershed level, so that on-site and off-site effects of seasonal concentration of livestock can be incorporated into developing feed production and management strategies for improving the system productivity and environmental protection